Oscillator circuits are used to convert dc power into a periodic waveform or signal. Conventional RC oscillators advantageously furnish a low-cost timing source and allow for generation of variable frequencies by changing the resistance R or capacitance C. Furthermore, conventional RC oscillators advantageously avoid the use of inductors, which are difficult to fabricate on integrated circuits.
Various circuit applications, such as instrumentation and mobile telecommunication applications, specify a very low current drain requirement. In these applications, a micropower RC oscillator is employed. One example of a conventional micropower RC oscillator is described in an article by P. Kakela et at. entitled "A Micropower RC Oscillator Chip for Consumer ASIC Applications", 6th Mediterranean Electrotechnical Conference Proceedings, pp. 278-81, V1; 1991. The Kakela et at. RC oscillator 100 is shown in FIG. 1 and includes a capacitor C and a resistor R, a circuit 110 for charging and discharging the capacitor C, a comparator 120 and a hysteresis circuit 130. The charging and discharging circuit 110 ramps the capacitor voltage up and down. The comparator 120 senses the voltage on the capacitor and the hysteresis circuit 130 changes the reference voltage of the comparator 120 and thereby causing the output voltage to switch state. Unfortunately, the frequency of oscillation of the RC oscillator 100 is significantly affected by the delay time within the comparator 120 and the hysteresis circuit 130 as opposed to a more advantageous situation in which the frequency of oscillation is determined by the R and C component values chosen for the circuit. Furthermore, the RC oscillator 100 operates at a current of approximately 2.mu.A while a much greater reduction is current is sought, for example a current range of approximately 200 nA to 300 nA.
What is needed is an RC oscillator circuit that operates with a very low supply current and operates with very short component delays so that the feedback loop of the oscillator is accelerated.